Cephalexin (Keflex)

Cephalexin in Brief

Active ingredient: cephalexin
Common brand names: Keflex, Keftabs, Biocef
Drug class: first-generation cephalosporin antibiotic
FDA Approved: January 4, 1971
Chemical Formula: C16H17N3O4S

FDA approved uses

Respiratory tract infections caused by Streptococcus pneumoniae and Streptococcus pyogenes
Otitis media due to Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcusaureus, Streptococcus pyogenes, and Moraxella catarrhalis
Skin and skin structure infections caused by Staphylococcusaureus and/or Streptococcus pyogenes
Bone infections caused by Staphylococcusaureus and/or Proteus mirabilis
Genitourinary tract infections, including acute prostatitis, caused by Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae

Cephalexin "pros" and "cons"

Advantages:

excellent safety record
very low incidence of allergic reactions
may be taken without regard to food
superior to penicillin in the streptococcal throat infection 2.
active against most gram-positive bacteria.

Disadvantages:

short half-life requires QID dosing: the serum half-life is 0.5–1.2 hours in adults, about 5 hours in neonates and 2.5 hours in children 3–12 months of age.
less active than cefatrizine and cefaclor against Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis 2.

Mode of action

Cephalexin inhibits the third and last stage of bacterial cell wall synthesis by preferably binding to specific proteins (PBPs) that are located inside the bacterial cell wall.

Time for Cephalexin to clear out the system

Cephalexin mean half-life is 50 to 80 min. It may take 4 to 5 hours to clear out of the system.

Further reading

Cephalexin (Keflex) versus other medications

References

1. Disney FA, Dillon H, Blumer JL, Dudding BA, McLinn SE, Nelson DB, Selbst SM. Cephalexin and penicillin in the treatment of group A beta-hemolytic streptococcal throat infections. Am J Dis Child. 1992 Nov;146(11):1324-7.
2. Luh KT, Chao HP, Ho SW, Hsieh WC. Comparison of in vitro antibacterial activity of four oral cephems: cephalexin, cefaclor, cefatrizine and cefadroxil. Zhonghua Min Guo Wei Sheng Wu Ji Mian Yi Xue Za Zhi. 1984 Feb;17(1):11-8. PubMed

Published: March 31, 2008
Last updated: April 25, 2011